Why Is AC-Current More Efficient Over Long Distances ?

[guest1289]

   Why Is AC-Current More Efficient Over Long Distances ?

    I have never found the actual reason,  and the reason is not mentioned on the wikipedia page.

    Is it something like :
      -  dc-current causes more fatigue on the wire/material,  or,  causes it to heat up more than ac-current,  for some reason,   maybe just for the reason that ac-current gives the  conductor-material that short rest before current is sent in the opposite direction(  seems like the most probable answer )
      -  or,  is it possible that in  ac-current  at great distances,  there is some sort of crashing effect between currents going in different directions( in the wire, or in the field around the wire ),  which somehow actually generates surplus current,  or,  boosts current( it would affect the frequency or cause interference ),  the end result being that more  current arrives at the other end. ( they have equipment which cleans the interference of the received current ).   
            So could it be some sort of unofficially known overunity effect of  ac-current  particularly over long distances,   is it possible that it occurs past some sort of specific distance.
   
     It's certainly odd,  because I assume  ac-current  is a very strong emitter of  electromagnetic-radiation( radio signal ) while  steady/smooth  dc-current( from a battery at least ) would emit none,  and yet  ac-current  is more efficient  over long distances.
     
      -  or is it something to do with the electromagnetic-field  around the wire,  but I'm not referring to losses via radio transmission,  even though  initially they seem to be the same thing,   maybe something like friction between the electromagnetic-field and materials outside of the wire,  or something else.

[lancaIV]

This is not directly an answer to your question and statements,but since 2 decades there is an alternative for HVAC cables : https://library.e.abb.com/public/3325cb4054a22738c125766400471fd5/HVDC%20Light%20Cables%20for%20long%20distance%20grid%20connection.pdf

http://iopscience.iop.org/article/10.1088/1742-6596/507/3/032037/pdf

one handicap less:
https://www.forumforthefuture.org/greenfutures/articles/breakthrough-long-distance-power-transmission

Often our information stand-point is not up-to-date,or alternatives are not in use cause the common technology and material is only cheaper , this argument only in value because the mass-production from HVAC cables !
And new material can not give us the safety and warranty like the "old"one.

I think the direction for off-shore energy-farming and energy distribution will in future be based by HVDC !


Sincerely
            OCWL

[Cherryman]

I'm no expert.. I always did think it is because DC is pushing electricity along..  the further the more resistance ( as in a water hose)

AC However is not moving the whole distance, it vibrates, by changing the magnetic field at some Hz. the electricity moves enough in its own limited space to excite coils (in appliances)
Thats why AC doesnt handle earth leaks well, at that moment it starts flowing and the system can't handle that.


See it like this..


Take a large rock.. lets say 5 ton , you on one side.. a person on the other  and you want to communicate.
Lets try pushing first (DC )
push te rock for 5 minutes , you have a hard time, and as you move the rock along.. you will either need to supply more rock, or travel yourself. .if you succeed.. then you would be exhausted
Now you take a hammer and give it a whack...   Now the other person will detect sound and/or feel vibration. Thats easy to do with way more less energy.
nothing moved from its place.. and the only thing to replenish is the whack

[Magluvin]

Im going to take a lil stab at it.

Makes me wonder why and how the Edison dc gens putting out 3 to 4kv gets distributed and what level is the voltage at the home or business?

But AC being able to convert very high voltage down to lower high voltages and then finally down to consumer level voltages, allows for very high voltages to be on long distance lines with little loss due to very low amperage where even the use of alum wire with its added resistance compared to copper is virtually nill in added resistance when considering the very high voltage.

DC, especially back then, didnt have the ways we can convert it today. Iimagine the city wire layouts possibly were set in ways that there was equal lengths of wire, aprox, to each destination as to get a safer voltage level after voltage drop through the lines?? 

So AC with the use of transformers allows for very high voltage across long distances, thus very low loss, where as DC, imagine having to deal with that high voltage at the consumer end, if it were 100kv or even 50kv. By the time there is say 400v at the destination, a source of 3 to 4kv with that kind of a voltage drop is big in losses.  I dunno maybe they had high voltage dc motors that ran local gens to lower the dc voltage. Maybe they didnt get to that before AC took over.

Mags

[citfta]

Why is it so hard for people to just do a simple search for their answers?  Here is a fairly in depth article and discussion about the pros and cons of using AC for long distance power transfer.

https://www.quora.com/Why-is-alternating-current-better-for-long-distance-power-transmission-than-direct-current